Semiconductor heterostructure with multiple active regions

ABSTRACT

A semiconductor heterostructure for an optoelectronic device includes a base semiconductor layer having one or more semiconductor heterostructure mesas located thereon. One or more of the mesas can include a set of active regions having multiple main peaks of radiative recombination at differing wavelengths. For example, a mesa can include two or more active regions, each of which has a different wavelength for the corresponding main peak of radiative recombination. The active regions can be configured to be operated simultaneously or can be capable of independent operation. A system can include one or more optoelectronic devices, each of which can be operated as an emitter or a detector.

REFERENCE TO RELATED APPLICATIONS

The current application claims the benefit of U.S. ProvisionalApplication No. 62/403,052, filed on 30 Sep. 2017, which is herebyincorporated by reference.

TECHNICAL FIELD

The disclosure relates generally to semiconductor heterostructures, andmore particularly, to a semiconductor heterostructure having multipleactive regions.

BACKGROUND ART

Solid state optoelectronic devices are frequently used to sense changesin biological fluids and to analyze chemical substances. In particular,fluorescent analysis is frequently used to determine the chemicalcomponents present within a medium.

SUMMARY OF THE INVENTION

Aspects of the invention are directed to the design and/or fabricationof a solid state optoelectronic device having multiple active regions.In an embodiment, such devices and a system of one or more of suchdevices can provide effective fluorescent analysis using multiplewavelengths, in particular wavelengths in the ultraviolet range. Furtheraspects of the invention are directed to a tandem of a multi-wavelengthlight emitting diode and a multi-wavelength photodiode, e.g., forfluorescent analysis and/or sensing applications.

An embodiment of a device described herein can have a semiconductorheterostructure containing several active regions. Each active region inthe semiconductor heterostructure can have a corresponding main peak ofradiative recombination at a different peak wavelength. In this case,the device can provide multiple solidly connected active regions capableof operating as an emitter and/or a detector at several peak wavelengthssimultaneously. In another embodiment, a semiconductor heterostructurecan include an active region that includes subsets of quantum wellshaving corresponding main peaks of radiative recombination at differentpeak wavelengths. In either case, the device can be capable of operatingas an emitter and/or a detector at several peak wavelengthssimultaneously.

Aspects of the invention provide a semiconductor heterostructure for anoptoelectronic device includes a base semiconductor layer having one ormore semiconductor heterostructure mesas located thereon. One or more ofthe mesas can include a set of active regions having multiple main peaksof radiative recombination at differing wavelengths. For example, a mesacan include two or more active regions, each of which has a differentwavelength for the corresponding main peak of radiative recombination.The active regions can be configured to be operated simultaneously orcan be capable of independent operation. A system can include one ormore optoelectronic devices, each of which can be operated as an emitteror a detector.

A first aspect of the invention provides a semiconductor heterostructurecomprising: a base semiconductor layer having a plurality of physicallyseparate semiconductor heterostructure mesas located thereon, whereineach of the plurality of mesas includes at least one active regionhaving a main peak of radiative recombination, and wherein at least oneof the plurality of mesas includes: a first active region having a firstmain peak of radiative recombination at a first wavelength and a firstfull width at half maximum; and a second active region having a secondmain peak of radiative recombination at a second wavelength and a secondfull width at half maximum, wherein the first wavelength and the secondwavelength differ by at least a larger of the first full width at halfmaximum or the second full width at half maximum.

A second aspect of the invention provides an optoelectronic devicecomprising: a base semiconductor layer having a semiconductorheterostructure mesa located on a first surface of the basesemiconductor layer, wherein the mesa includes a plurality of activeregions, each active region having a main peak of radiativerecombination, and wherein the plurality of active regions include: afirst active region having a first main peak of radiative recombinationat a first wavelength and a first full width at half maximum; and asecond active region having a second main peak of radiativerecombination at a second wavelength and a second full width at halfmaximum, wherein the first wavelength and the second wavelength differby at least a larger of the first full width at half maximum or thesecond full width at half maximum.

A third aspect of the invention provides a system comprising: a firstoptoelectronic device comprising: a base semiconductor layer having asemiconductor heterostructure mesa located on a first surface of thebase semiconductor layer, wherein the mesa includes a plurality ofactive regions, each active region having a main peak of radiativerecombination, and wherein the plurality of active regions include: afirst active region having a first main peak of radiative recombinationat a first wavelength and a first full width at half maximum; and asecond active region having a second main peak of radiativerecombination at a second wavelength and a second full width at halfmaximum, wherein the first wavelength and the second wavelength differby at least a larger of the first full width at half maximum or thesecond full width at half maximum; and a second optoelectronic device,wherein one of the first or second optoelectronic devices is configuredto be operated as an emitter and the other of the first or secondoptoelectronic devices is configured to be operated as a detector.

The illustrative aspects of the invention are designed to solve one ormore of the problems herein described and/or one or more other problemsnot discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various aspects of the invention.

FIG. 1 shows a schematic of an illustrative optoelectronic deviceaccording to an embodiment.

FIGS. 2A-2D show an illustrative series of fabrication acts forfabricating an optoelectronic device according to an embodiment.

FIGS. 3A-3E show an illustrative series of fabrication acts forfabricating a heterostructure using progressive masking to form mesasaccording to an embodiment.

FIG. 4 shows an illustrative device including a mesa with cavitiesformed therein according to an embodiment.

FIG. 5 shows an illustrative device including contact layers formed onthe sidewalls of a mesa according to an embodiment.

FIGS. 6A and 6B show variations of devices having a mesa with lateralcurrent injection according to embodiments.

FIG. 7 shows still another device according to an embodiment.

FIGS. 8A and 8B show illustrative two- and three-dimensional views,respectively, of illustrative portions of an optoelectronic deviceaccording to an embodiment.

FIG. 9 shows an illustrative system including an optoelectronic deviceconfigured to be operated as an emitter and an optoelectronic deviceconfigured to be operated as a detector according to an embodiment.

FIG. 10 shows a three-dimensional view of an illustrative system, whichincludes three emitters and three detectors all of which are coupled toa channel region, according to an embodiment.

FIGS. 11A and 11B show two illustrative time dependent operation of anemitter and detector in a system according to embodiments.

FIG. 12 shows an illustrative flow diagram for fabricating a circuitaccording to an embodiment.

It is noted that the drawings may not be to scale. The drawings areintended to depict only typical aspects of the invention, and thereforeshould not be considered as limiting the scope of the invention. In thedrawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide a semiconductorheterostructure for an optoelectronic device includes a basesemiconductor layer having one or more semiconductor heterostructuremesas located thereon. One or more of the mesas can include a set ofactive regions having multiple main peaks of radiative recombination atdiffering wavelengths. For example, a mesa can include two or moreactive regions, each of which has a different wavelength for thecorresponding main peak of radiative recombination. The active regionscan be configured to be operated simultaneously or can be capable ofindependent operation. A system can include one or more optoelectronicdevices, each of which can be operated as an emitter or a detector.

As used herein, unless otherwise noted, the term “set” means one or more(i.e., at least one) and the phrase “any solution” means any now knownor later developed solution. It is understood that, unless otherwisespecified, each value is approximate and each range of values includedherein is inclusive of the end values defining the range. As usedherein, unless otherwise noted, the term “approximately” is inclusive ofvalues within +/− ten percent of the stated value, while the term“substantially” is inclusive of values within +/− five percent of thestated value.

As also used herein, a layer is a transparent layer when the layerallows at least ten percent of radiation having a target wavelength,which is radiated at a normal incidence to an interface of the layer, topass there through. Furthermore, as used herein, a layer is a reflectivelayer when the layer reflects at least ten percent of radiation having atarget wavelength, which is radiated at a normal incidence to aninterface of the layer. In an embodiment, the target wavelength of theradiation corresponds to a wavelength of radiation emitted or sensed(e.g., peak wavelength +/− five nanometers) by an active region of anoptoelectronic device during operation of the device. For a given layer,the wavelength can be measured in a material of consideration and candepend on a refractive index of the material. Additionally, as usedherein, a contact is considered “ohmic” when the contact exhibits closeto linear current-voltage behavior over a relevant range ofcurrents/voltages to enable use of a linear dependence to approximatethe current-voltage relation through the contact region within therelevant range of currents/voltages to a desired accuracy (e.g., +/− onepercent).

Turning to the drawings, FIG. 1 shows a schematic of an illustrativeoptoelectronic device 10 according to an embodiment. The device 10 isshown including a base semiconductor layer 12 located on a substrate 11.A plurality of mesas 14A-14C are located on the base semiconductor layer12. Each mesa 14A-14C includes a corresponding region 13A-13C of thebase semiconductor layer 12 located at the bottom of the mesa 14A-14C,followed by one or more active regions 16A-16C. Each active region16A-16C in a mesa 14A-14C is bounded by one or more semiconductor layers18A-18C. Each mesa 14A-14C can further include a correspondingsemiconductor contact layer 20A-20C and a corresponding contact 22A-22C.

In an embodiment, the base semiconductor layer 12 comprises asemiconductor layer having one of an n-type or a p-type conductivity. Inthis case, the device 10 can include a set of contacts 24A-24D to thebase semiconductor layer 12. For example, as illustrated, contacts24A-24D can be located directly on the same surface of the basesemiconductor layer 12 as the mesas 14A-14C in regions where the mesas14A-14C are not present. While each contact 24A-24D is shown as beingphysically separated from the mesas 14A-14C, it is understood that asidewall of a contact 24A-24D can contact a sidewall of one or moremesas 14A-14C, e.g., the sidewall of one or more of the regions 13A-13Cof the base semiconductor layer 12. In a more particular embodiment, thebase semiconductor layer 12 is an n-type semiconductor contact layer andthe contacts 24A-24D are n-type contacts. In this case, thesemiconductor contact layer 20A-20C in each mesa 14A-14C can be a p-typesemiconductor contact layer and the contacts 22A-22C can be p-typecontacts.

The device 10 can comprise any type of optoelectronic device. In anembodiment, the optoelectronic device 10 is configured to operate as anemitting device, such as a light emitting diode (LED) or a laser diode(LD), having multiple peak emission wavelengths. Alternatively, theoptoelectronic device 10 can operate as a sensing device, such as aphotodiode, sensitive at multiple peak sensing wavelengths. Stillfurther, the optoelectronic device 10 can be configured to concurrentlyoperate as an emitting and sensing device. Regardless, during operationof the optoelectronic device 10, application of a bias to the p-type andn-type contacts 22A-22C, 24A-24D comparable to the band gap can resultin the emission of electromagnetic radiation from one or more of theactive regions 16A-16C of the optoelectronic device 10. Alternatively,impingement of electromagnetic radiation on one or more of the activeregions 16A-16C can result in a bias in one or more of the activeregions 16A-16C, which can be detected at the p-type and n-type contacts22A-22C, 24A-24D.

In an embodiment, one or more of the active regions 16A-16C is formedfrom a series of alternating quantum wells and barriers. Theelectromagnetic radiation emitted or sensed by each active region16A-16C of the optoelectronic device 10 can have a peak wavelengthwithin any range of wavelengths, including visible light, ultravioletradiation, deep ultraviolet radiation, infrared light, and/or the like.In an embodiment, one or more of the active regions 16A-16C of thedevice 10 is configured to emit or sense radiation having a dominantwavelength within the ultraviolet range of wavelengths. In a morespecific embodiment, the dominant wavelength is within a range ofwavelengths between approximately 210 and approximately 360 nanometers(between approximately 250 and approximately 310 nanometers in a stillmore specific embodiment).

Each active region 16A-16C can be designed such that a main peak ofradiative recombination has a target peak wavelength. In an embodiment,the first active region 16A can have first composition and thickness ofquantum wells and barriers; whereas the second active region 16B canhave a different composition and/or thickness of quantum wells andbarriers resulting in different radiation or absorption properties ofthe active region 16B as compared to the active regions 16A. To thisextent, each active region 16A-16C in a mesa 14A-14C can beindependently designed to have a corresponding target peak wavelength.In an embodiment, the first, second, third, etc., active region 16A-16Cin each mesa 14A-14C is configured to have the same peak wavelength.However, it is understood that this is not necessary, and each activeregion in each mesa can be uniquely configured. Furthermore, it isunderstood that embodiments of the device 10 can include any combinationof active regions, including all active regions, which are configured tohave the same target peak wavelength.

When the peak wavelengths for two or more active regions of a mesadiffer, the peak wavelengths can differ by an amount that exceeds anyunintentional difference that results from a manufacturing process usedin fabricating the device 10. For example, two active regions can havefirst and second main peaks of radiative recombination at first andsecond wavelengths and first and second full widths at half maximum,respectively. In an embodiment, the first wavelength and the secondwavelength differ by at least a larger of the first full width at halfmaximum (FWHM) or the second full width at half maximum. In anembodiment, the first and second wavelengths can be in distinct regions(e.g., visible, ultraviolet, infrared, etc.) of the electromagneticspectrum.

In an illustrative embodiment, the optoelectronic device 10 is a groupIII-V materials based device, in which some or all of the varioussemiconductor layers are formed of elements selected from the groupIII-V materials system. In a more particular illustrative embodiment,the various layers of the optoelectronic device 10 are formed of groupIII nitride based materials. Group III nitride materials comprise one ormore group III elements (e.g., boron (B), aluminum (Al), gallium (Ga),and indium (In)) and nitrogen (N), such that B_(w)Al_(x)Ga_(y)In_(z)N,where 0≤w, x, y, z≤1, and w+x+y+z=1. Illustrative group III nitridematerials include binary, ternary and quaternary alloys such as, AIN,GaN, InN, BN, AlGaN, AlInN, AlBN, AlGaInN, AlGaBN, AlInBN, and AlGaInBNwith any molar fraction of group III elements.

Illustrative group III nitride based active regions 16A-16C includeIn_(y)Al_(x)Ga_(1-x-y)N, Ga_(z)In_(y)Al_(x)B_(1-x-y-z)N, anAl_(x)Ga_(1-x)N semiconductor alloy, or the like. Similarly, each of thevarious semiconductor layers 12, 18A-18C, 20A-20C of the device 10 canbe composed of an In_(y)Al_(x)Ga_(1-x-y)N alloy, aGa_(z)In_(y)Al_(x)B_(1-x-y-z)N alloy, or the like. The molar fractionsgiven by x, y, and z can vary between the various layers 12, 16A-16C,18A-18C, 20A-20C. The molar fractions can be selected based on thedesired attributes of the layer and/or the corresponding wavelength forelectromagnetic radiation corresponding to the optoelectronic device 10.For example, the molar fractions for the active regions 16A-16C can beselected to emit and/or sense electromagnetic radiation of a targetwavelength, while the molar fractions for the remaining layers 12,18A-18C, 20A-20C can be selected to result in manageable stresses in theactive regions 16A-16C. It is understood that embodiments of theoptoelectronic device 10 can include multiple layers for one or more ofthe semiconductor layers 12, 18A-18C, 20A-20C shown and describedherein.

The substrate 11 can be composed of a material that is transparent tothe electromagnetic radiation corresponding to (e.g., emitted or sensedby) the optoelectronic device 10. Additionally, the substrate 11 can beformed of a material suitable for growth of the correspondingsemiconductor (e.g., group III nitride) materials thereon. To thisextent, an embodiment of the substrate 11 is formed of sapphire.However, it is understood that the substrate 11 can be formed of anysuitable material including, for example, silicon carbide (SiC), silicon(Si), bulk GaN, bulk AIN, bulk or a film of AlGaN, bulk or a film of BN,AlON, LiGaO₂, LiAlO₂, aluminum oxinitride (AlO_(x)N_(y)), MgAl₂O₄, GaAs,Ge, or another suitable material. Furthermore, one or more surfaces ofthe substrate 11 can be substantially flat or patterned using anysolution. Such patterning can be designed to facilitate quality growthof a semiconductor layer thereon and/or passage of electromagneticradiation through the surface.

Each of the semiconductor layers in the mesas 14A-14C can be configuredto provide any type of desired functionality. For example, asemiconductor layer 12, 18A-18C adjacent to the active region 16A-16Cclosest to the n-type side of the device can comprise a cladding layer,an electron supply layer, a contact layer, and/or the like. Similarly, asemiconductor layer 12, 18A-18C adjacent to the active region 16A-16Cclosest to the p-type side of the device can comprise an electronblocking layer, a cladding layer, a hole supply layer, a contact layer,and/or the like.

In an embodiment the p-n junction is fabricated in the top portion ofeach mesa 14A-14C, resulting in significant luminescence of the topactive layer in the corresponding mesa, e.g., active layer 16C in themesa 14A, active layer 16B in the mesa 14B, and active layer 16A in themesa 14C. With such a configuration, a semiconductor layer locatedbetween two active layers, such as the semiconductor layer 18A in mesas14A, 14B and the semiconductor layer 18B in the mesa 14A, can be n-typedoped, while the topmost semiconductor layer (e.g., semiconductor layer18C in the mesa 14A) is p-type doped. Regardless, the n-typesemiconductor layers of the device 10 can be configured to betransparent to the radiation corresponding to any one of the activelayers 16A-16C. To this extent, a bandgap for each n-type semiconductorlayer can be wider than the bandgap of any of the quantum wells in anyof the active layers 16A-16C.

In an embodiment, one or more of the semiconductor layers 12, 18A-18Ccan comprise a short period superlattice lattice structure, such as anat least partially transparent magnesium (Mg)-doped AlGaN/AlGaN shortperiod superlattice structure (SPSL) on the p-type side or an AlGaN SPSLon the n-type side, which is transparent to the electromagneticradiation generated and/or sensed by the active regions 16A-16C. In anembodiment, an n-type semiconductor layer, such as the basesemiconductor layer 12 or a contact layer 20A-20C, is n-type doped witha carrier concentration being at least 10¹⁷ 1/cm³. In an embodiment thep-type doping can be at least 10¹⁷ 1/cm³, and more particularly in arange of approximately 10¹⁸-10¹⁹ 1/cm³. In an embodiment, a p-typelayer, such as the base semiconductor layer 12 or the contact layer20A-20C, can comprise a p-type doped GaN, p-type AlGaN, a p-typeAl_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N semiconductor superlattice, with x and yvalues being different by at least 1% but preferably by 5% or more,and/or the like.

Each contact 22A-22C, 24A-24D can form an ohmic contact to thecorresponding semiconductor layer. In an embodiment, one or more of thecontacts 22A-22C, 24A-24D comprises several conductive and reflectivemetal layers. Alternatively, one or more of the contacts 22A-22C,24A-24D can comprise a highly conductive metal.

It is understood that the device 10 is only illustrative of variouspossible configurations for a device described herein. For example, thenumber of and layer configurations of mesas 14A-14C are onlyillustrative. To this extent, a device described herein can includeadditional semiconductor layers in the heterostructure, fewersemiconductor layers, and/or different configurations of semiconductorlayers. An illustrative semiconductor layer can comprise a buffer layer,which can be epitaxially grown directly on the substrate 11. The basesemiconductor layer 12 can subsequently be epitaxially grown on thebuffer layer. For an illustrative group III nitride basedheterostructure, such a buffer layer can comprise an AlN layer and thebase semiconductor layer 12 can comprise an n-type AlGaN layer.

A device described herein can be fabricated using any solution. FIGS.2A-2D show an illustrative series of fabrication acts for fabricating anoptoelectronic device according to an embodiment. As illustrated in FIG.2A, a semiconductor heterostructure can be formed, which includes a basesemiconductor layer 12, multiple active regions 16A-16C, and interveningsemiconductor layers 18A-18C using any growth solution. For example, thevarious semiconductor layers can be epitaxially grown on a substrate 11(FIG. 1) using any epitaxial growth solution.

Subsequently, the semiconductor heterostructure can be selectivelyetched to form the mesas 14A-14C, each of which is located directly on asurface of the base semiconductor layer 12. As illustrated, the etchingcan extend into a top surface of the base semiconductor layer 12 inregions located between the mesas 14A-14C. Additionally, the amount ofetching can vary among the mesas 14A-14C. To this extent, the etchingcan include removing one or more of the originally grown semiconductorlayers 18A-18C and/or active regions 16A-16C from one or more of themesas 14A-14C.

In an embodiment, the etching process includes selectively addingmasking materials after a desired amount of material has been etched.For example, initially, a masking material can be applied to a topsurface of the mesa 14A and the remainder of the semiconductorheterostructure can be etched. The etching can continue until the adesired top of the second mesa 14B, at which time a masking material canbe applied to the top of the second mesa 14B and etching can resume.Subsequently, once exposed, a masking material can be applied to a topsurface for the third mesa 14C and etching can resume until a desiredamount of the base semiconductor layer 12 has been etched. Subsequently,the masking material can be removed from the top surface of each mesa14A-14C using any solution. The etching can be performed using ansuitable etching process, such as reactive ion etching, dry etching inCl₂/N₂/O₂ plasma or Cl₂/Ar based inductively coupled plasma, and/or thelike. The masking material can comprise any suitable masking material,such as any of various photoresists known in the art.

As illustrated in FIG. 2C, one or more semiconductor layers, such as thecontact layers 20A-20C, can be formed on the mesas 14A-14C using anysolution. For example, the contact layers 20A-20C can be formed using anepitaxial overgrowth process. In this case, a photolithographic mask canbe applied to the regions between the mesas 14A-14C to prevent growth ofthe semiconductor thereon. Subsequently, the contact layers 20A-20C canbe grown on the top surface of each mesa 14A-14C, followed by theremoval of the photoresist material from the surfaces of the basesemiconductor layer 12 using any suitable photoresist removal solventknown in the art.

In FIG. 2D, the metal contacts, such as metal contacts 22A, 24A, aredeposited over the corresponding semiconductor layers. For example,metal contacts 24A (e.g., n-type contacts) can be deposited on thesurface of the base semiconductor layer 12, while metal contacts 22A(e.g., p-type contacts) can be deposited on the surface of each contactlayer 20A-20C. The metal contacts can be selected depending on the typeof ohmic contact (n-type or p-type) for the corresponding metal contact.For example, the metal contacts 24A can comprise n-type metal(s) such asTi, Al, and/or the like, while the metal contacts 22A can comprisep-type metal(s) such as Ni, Pd, and/or the like. The metal contacts 22A,24A can be deposited using a photolithographic process throughevaporation or sputtering.

It is understood that the growth process shown in FIGS. 2A-2D is onlyillustrative of various possible growth processes. In an embodiment,such as when the p-n junction is formed in the top portion of each mesa,only the various semiconductor layers of a first type of doping, e.g.,n-type doping, can be grown prior to performing the etching shown inFIG. 2B. For example, as discussed herein, when the semiconductor layer18C is p-type doped, growth of the semiconductor layer 18C can occurafter etching, e.g., prior to the growth of the contact layers 20A-20Cas shown in FIG. 2C.

FIGS. 3A-3E show an illustrative series of fabrication acts forfabricating a heterostructure using progressive masking to form mesasaccording to an embodiment. In this case, as shown in FIG. 3A, the basesemiconductor layer 12 can be grown, followed by deposition of maskinglayers 15A-15D on the regions of the base semiconductor layer 12 thatwill be located between the mesas. As shown in FIG. 3B, the regions13A-13C and the active layer 16A can be grown, followed by depositing amasking layer 15E on the active region 16A in the third mesa. Next, asshown in FIG. 3C, semiconductor layer 18A and active region 16B can begrown, followed by depositing a masking layer 15F on the active region16B in the second mesa. As shown in FIG. 3D, the semiconductor layer 18Band active region 16C can be grown, followed by removal of the maskinglayers 15E, 15F from the other mesas. In FIG. 3E, the semiconductorlayer 18C can be grown on each mesa with a doping (e.g., p-type)opposite that of the previously grown (e.g., n-type doped) semiconductorlayers. Further fabrication of the device can proceed similar to theprocess described in conjunction with FIGS. 2C and 2D.

Embodiments of a device described herein can be fabricated using one ormore cavities to provide access to an active region. For example, FIG. 4shows an illustrative device 30 including a mesa with cavities formedtherein according to an embodiment. In this case, the device 30 is shownincluding a single mesa 14 located directly on a surface of a basesemiconductor layer 12. The mesa 14 includes multiple active regions16A-16C, each of which has a corresponding contact layer 20A-20C andmetal contact 22A-22C thereto. Additionally, a metal contact 24 is shownlocated on the surface of the base semiconductor layer 12 next to themesa 14.

In an embodiment, the mesa 14 is formed by first forming (e.g., growing)the plurality of active regions 16A-16C and corresponding semiconductorlayers 18A-18C on the base semiconductor layer 12. Subsequently, aplurality of cavities can be formed in the mesa, each cavity extendingto a depth just above that of a corresponding active region 16A-16Cusing any solution (e.g., repeated acts of masking and etching followedby removal of the masking material). Next, the contact layers 20A-20Ccan be formed within the cavities, e.g., by epitaxial overgrowth.

When a cavity extends through one or more active regions to reach anunderlying active region, the sidewalls of the cavity can be coveredwith a dielectric material 26A, 26B using any solution, such assputtering, chemical vapor deposition (CVD), etc. The dielectricmaterial can comprise any suitable dielectric material, such as silicondioxide, silicon nitride, aluminum nitride, and/or the like.Subsequently, the metal contacts 22A-22C can be formed (e.g., deposited)in the cavities using any solution.

While the device 30 is shown including a single mesa 14, it isunderstood that embodiments of a device described herein can include anynumber of mesas, each of which includes one or more active regions.Additionally, for each such mesa including multiple active regions, themesa can include multiple contacts 22A-22C formed in cavities in themesa as shown in conjunction with the device 30. To this extent, anembodiment of the device 10 shown in FIG. 1 can include a mesa, such asthe mesa 14A, including cavities and multiple contacts 22A-22C as shownin conjunction with the device 30.

In an embodiment, a sidewall of a mesa can be used to provide access tothe multiple active regions located therein. To this extent, FIG. 5shows an illustrative device 32 including semiconductor contacts layers20A, 20B formed on the sidewalls of a mesa 14 according to anembodiment. In this case, the mesa 14 includes active regions 16A-16C,which are separated by semiconductor layers 18A, 18B that can contain nointentional doping. The base semiconductor layer 12 in this embodimentcan comprise a buffer layer. As discussed herein, each active region16A-16C can be configured to operate at a distinct peak wavelength.Current is injected laterally through the semiconductor contact layers20A, 20B formed on the side walls of the mesa 14 with the p-n junctionformed laterally.

In an embodiment, the semiconductor contact layer 20A can comprise ann-type semiconductor contact layer (e.g., n-type cladding layer) thatcan be epitaxially overgrown over a first side of the mesa 14, while thesemiconductor contact layer 20B can comprise a p-type semiconductorcontact layer (e.g., p-type cladding layer) that can be epitaxiallyovergrown over a second side of the mesa 14. The epitaxial overgrowthcan be improved when the mesa 14 has inclined sidewalls as illustrated.In an embodiment, the angle of inclination of at least a portion of asidewall of the mesa 14 can be between 10 to 80 degrees. However, it isunderstood that other angles (including vertical sidewalls) can beutilized. The mesa 14 can be fabricated by first growing a semiconductorheterostructure and then etching to form the mesa 14. Such etching canbe due to particular composition of layers as is known in the art. Forexample, the etching of GaN layers has a higher rate than etching ofAlGaN layers with high composition of AlN.

The n-type and p-type semiconductor contact layers 20A, 20B can becontacted by corresponding metallic contacts, which can be operated toresult in current passing through the mesa 14. For efficient operationof the mesa 14, the lateral dimension (e.g., maximum lateral distance)between the n-type and p-type semiconductor contact layers 20A, 20B canbe comparable to the carrier diffusion length within the active regions16A-16C, such as the hole diffusion length, as it is the smallestdiffusion length in the device. As used herein, the lateral dimension iscomparable to the hole diffusion length with it is within an order ofmagnitude of the hole diffusion length. To this extent, the lateraldimension can be several times larger or smaller than the hole diffusionlength. It is understood that due to sufficiently wide ranges, the holediffusion length can be taken as the smallest hole diffusion lengthcalculated over all the layers of the semiconductor heterostructure ofall the active regions presented in the device. The hole diffusionlength can be calculated as √{square root over (Dτ)}, where D is thediffusion coefficient and τ is the carrier lifetime. The diffusioncoefficient is directly proportional to the mobility of the carrierswithin the semiconductor heterostructure. It is feasible for the mesa 14to have sub-micron or micron lateral dimension, for optimal operation ofthe lateral injection within the mesa 14.

FIGS. 6A and 6B show variations of devices 34A, 34B, respectively,having a mesa 14 with lateral current injection according toembodiments. In each case, metal contacts 22, 24 are formed adjacent tothe semiconductor contact layers 20A, 20B, respectively. In anembodiment, the angle of the slanted sides of the mesa 14 shown in FIG.6A can be selected to improve light extraction and/or absorptioncharacteristics of the mesa. The device 34B is shown including a mesa 14having vertical sidewalls, which can be easier to manufacture.

In each case, the mesa 14 can include a single active region 16, whichcan be configured to simultaneously emit or detect multiple wavelengthsof radiation. For example, the active region 16 can comprise a multiplequantum well structures with subsets of quantum wells configured to emitor detect different wavelengths of radiation. Furthermore, the activeregion 16 can include interlayers, which can be configured to improvestress management of the corresponding device 34A, 34B. The interlayerscan comprise semiconductor layers having a sub-nanometer thickness, suchas a few atomic layers. In general, the composition of the interlayerscan be chosen to differ from neighboring layers to provide a latticemismatch that can be used for stress control for neighboringsemiconductor layers. In an embodiment, the active region 16 cancomprise group III nitride semiconductor layers comprising AlInBGaNsemiconductors with the selected molar fractions of each semiconductormaterial configured for optimal emission or detection characteristics ofthe layer.

While the devices 32, 34A, 34B are each shown including a single mesa14, it is understood that embodiments of a device described herein caninclude any number of mesas. Additionally, one or more of the mesas caninclude semiconductor contact layers 20A, 20B formed on the sidewallsthereof, with current being injected laterally. To this extent, anembodiment of the device 10 shown in FIG. 1 can include mesas 14A-14Chaving semiconductor contact layers 20A, 20B formed on the sidewallsthereof as shown in conjunction with one or more of the devices 32, 34A,34B.

FIG. 7 shows still another device 36 according to an embodiment. In thiscase, similar to the device 10 shown in FIG. 1, the device 36 includesseveral mesas 14A-14H, each of which can include one or more activeregions, a semiconductor contact layer, and a metal contact (e.g.,p-type), as described herein. In this embodiment, a plurality ofmetallic contacts 24 (e.g., n-type) are formed on an opposite side ofthe base semiconductor layer 12 as the mesas 14A-14H. While multiplemetallic contacts 24 are shown, it is understood that any number of oneor more metallic contacts 24 can be formed adjacent to the basesemiconductor layer 12. When the base semiconductor layer 12 isfabricated on a substrate 11 (FIG. 1), the substrate can be detachedusing any solution, such as an appropriate lift-off process, prior todeposition of the metallic contacts 24. Additionally, the device 36 isshown including a protective layer 28, which can encapsulate at least aportion of the mesas 14A-14H. The protective layer 28 can be formed ofany suitable dielectric material, such as silicon dioxide, siliconnitride, aluminum nitride, and/or the like.

In a more particular embodiment, the mesas 14A-14H can comprise nano- ormicro-structures, such as nanowires. Each mesa 14A-14H can comprise apyramid or other appropriate three-dimensional object, and can befabricated using appropriate three-dimensional overgrowth techniques,through masking and overgrowth. through etching, and/or the like. Theoptoelectronic device 36 can have multiple active layers incorporatedinto the different nano-structure mesas 14A-14H. The use ofnano-structure mesas 14A-14H can result in an improvement to the lightextraction/absorption from/by the device 36.

FIGS. 8A and 8B show illustrative two- and three-dimensional views,respectively, of illustrative portions of an optoelectronic device 38according to an embodiment. In this embodiment, the mesas 14, such asthe mesas 14A-14C shown in FIG. 8A, can comprise one or more laterallyinjected active regions. In an embodiment, the mesas 14A-14C arefabricated through patterning followed by layer deposition. For example,the patterning can be first performed of the semiconductorheterostructure to result in mesas 14A-14C using photolithography andetching, followed by deposition of layers 20A and 20B.

Subsequently, an n-type semiconductor contact layer 20A or a p-typesemiconductor contact layer 20B can be deposited into the valleyslocated between the mesas 14A-14C. As illustrated, the n-type and p-typesemiconductor contact layers 20A, 20B can be deposited such that eachvalley includes only a single type of semiconductor contact layer andeach mesa 14A-14C is adjoined by both types of semiconductor layers 20A,20B. To this extent, the n-type and p-type semiconductor contact layers20A, 20B can be deposited in alternating valleys located between themesas 14A-14C. Subsequently, the n-type and p-type metal contacts 22,24, respectively, can be deposited over the corresponding n-type andp-type semiconductor contact layers 20A, 20B.

An embodiment provides a system that includes one or more optoelectronicdevices described herein. For example, an optoelectronic devicedescribed herein can be utilized as an emitter, and can be operated inconjunction with one or more detectors. Alternatively, an optoelectronicdevice described herein can be utilized as a detector, and can beoperated in conjunction with one or more emitters. A more particularembodiment provides a system that includes multiple optoelectronicdevices described herein. In such a system, one or more of theoptoelectronic devices can be configured to operate as an emitter, whileone or more of the optoelectronic devices can be configured to operateas a detector. However, it is understood that embodiments of a systemcan include multiple optoelectronic devices described herein that areconfigured to be operated only as one of emitters or detectors.

FIG. 9 shows an illustrative system 40 including a first optoelectronicdevice 42 configured to be operated as an emitter (e.g., a laser) and asecond optoelectronic device 44 configured to be operated as a detectoraccording to an embodiment. The system 40 is further shown including achannel region 46, to which the optoelectronic devices 42, 44 can beattached. During operation of the system 40, the emitter 42 can emitradiation having a first set of peak wavelengths and the detector 44 candetect radiation having a second set of peak wavelengths. The radiationemitted by the emitter 42 can be directed into the channel region 46,which can include a medium 48 that emits a fluorescent signal inresponse to the radiation. The detector 44 can be configured to detectthe resulting fluorescent signal excited by the radiation. The detectedfluorescent signal can be processed to analyze one or more (e.g.,optical, photoluminescence, and/or the like) properties of the medium48. For example, the medium 48 can comprise a fluorescent liquid to beevaluated, which is flowing through the channel region 46, such as urineor another fluorescent liquid.

The peak wavelength(s) for each device 42, 44 can be the same or some orall of the peak wavelengths can differ. To this extent, the activeregions of the detector 44 can differ from the active regions of theemitter 42. Additionally, while each device 42, 44 is shown having aconfiguration similar to the optoelectronic device shown in FIG. 1, itis understood that each device 42, 44 can have any configuration asdescribed herein and both devices 42, 44 can have differentconfigurations.

While the system 40 is shown including two optoelectronic devices 42,44, it is understood that embodiments of a system described herein caninclude any number of optoelectronic devices 42, 44. For example, FIG.10 shows a three-dimensional view of an illustrative system 50, whichincludes three emitters 42A-42C and three detectors 44A-44C all of whichare coupled to a channel region 46, according to an embodiment. In thiscase, each emitter 42A-42C can be configured to excite a fluorescentsignal in a medium located in the channel region 46, which can bedetected by a corresponding detector 44A-44C. While the system 50 isshown including emitters and detectors implemented in a one-to-onecorrespondence, it is understood that this need not be the case andembodiments of a system described herein can include a different numberof emitters and detectors. Furthermore, it is understood that thearrangement of emitters and detectors shown in the system 50 is onlyillustrative and any suitable arrangement of emitters and detectors canbe implemented.

The emitter(s) and detector(s) in a system described herein can beoperated in using any of various operation protocols. In an embodiment,the emitter(s) and detector(s) are operated using any one of varioustime dependent operation protocols, which can enable time dependentfluorescent analysis. To this extent, FIGS. 11A and 11B show twoillustrative time dependent operation of an emitter and detector in asystem according to embodiments. As illustrated in FIG. 11A, the emittercan release a pulse of radiation having a particular wavelength ormultiple wavelengths as a first time. Subsequently, the detector cananalyze a time dependent fluorescent signal that is generated inresponse to the pulse. One or more attributes of the detectedfluorescent signal, such as the time shift of the signal, can beanalyzed. The time shift corresponds to the time passed between initialexcitation and the resulting fluorescent response, and can be indicativeof one or more properties of the substance being analyzed. As shown inFIG. 11B, the emitter an operate in a time periodic manner to emitradiation having varying intensity over time and the detector can detecta periodic fluorescent signal, which results from the emitted radiation.One or more attributes of the detected fluorescent signal, such as thephase shift of the signal, can be analyzed. The phase shift is similarto the time shift, but for periodic excitation, and also can beindicative of one or more properties of the substance being analyzed.

While illustrative aspects of the invention have been shown anddescribed herein primarily in conjunction with a heterostructure for anoptoelectronic device and a method of fabricating such a heterostructureand/or device, it is understood that aspects of the invention furtherprovide various alternative embodiments.

In one embodiment, the invention provides a method of designing and/orfabricating a circuit that includes one or more of the devices designedand fabricated as described herein. To this extent, FIG. 12 shows anillustrative flow diagram for fabricating a circuit 126 according to anembodiment. Initially, a user can utilize a device design system 110 togenerate a device design 112 for a semiconductor device as describedherein. The device design 112 can comprise program code, which can beused by a device fabrication system 114 to generate a set of physicaldevices 116 according to the features defined by the device design 112.Similarly, the device design 112 can be provided to a circuit designsystem 120 (e.g., as an available component for use in circuits), whicha user can utilize to generate a circuit design 122 (e.g., by connectingone or more inputs and outputs to various devices included in acircuit). The circuit design 122 can comprise program code that includesa device designed as described herein. In any event, the circuit design122 and/or one or more physical devices 116 can be provided to a circuitfabrication system 124, which can generate a physical circuit 126according to the circuit design 122. The physical circuit 126 caninclude one or more devices 116 designed as described herein.

In another embodiment, the invention provides a device design system 110for designing and/or a device fabrication system 114 for fabricating asemiconductor device 116 as described herein. In this case, the system110, 114 can comprise a general purpose computing device, which isprogrammed to implement a method of designing and/or fabricating thesemiconductor device 116 as described herein. Similarly, an embodimentof the invention provides a circuit design system 120 for designingand/or a circuit fabrication system 124 for fabricating a circuit 126that includes at least one device 116 designed and/or fabricated asdescribed herein. In this case, the system 120, 124 can comprise ageneral purpose computing device, which is programmed to implement amethod of designing and/or fabricating the circuit 126 including atleast one semiconductor device 116 as described herein.

In still another embodiment, the invention provides a computer programfixed in at least one computer-readable medium, which when executed,enables a computer system to implement a method of designing and/orfabricating a semiconductor device as described herein. For example, thecomputer program can enable the device design system 110 to generate thedevice design 112 as described herein. To this extent, thecomputer-readable medium includes program code, which implements some orall of a process described herein when executed by the computer system.It is understood that the term “computer-readable medium” comprises oneor more of any type of tangible medium of expression, now known or laterdeveloped, from which a stored copy of the program code can beperceived, reproduced, or otherwise communicated by a computing device.

In another embodiment, the invention provides a method of providing acopy of program code, which implements some or all of a processdescribed herein when executed by a computer system. In this case, acomputer system can process a copy of the program code to generate andtransmit, for reception at a second, distinct location, a set of datasignals that has one or more of its characteristics set and/or changedin such a manner as to encode a copy of the program code in the set ofdata signals. Similarly, an embodiment of the invention provides amethod of acquiring a copy of program code that implements some or allof a process described herein, which includes a computer systemreceiving the set of data signals described herein, and translating theset of data signals into a copy of the computer program fixed in atleast one computer-readable medium. In either case, the set of datasignals can be transmitted/received using any type of communicationslink.

In still another embodiment, the invention provides a method ofgenerating a device design system 110 for designing and/or a devicefabrication system 114 for fabricating a semiconductor device asdescribed herein. In this case, a computer system can be obtained (e.g.,created, maintained, made available, etc.) and one or more componentsfor performing a process described herein can be obtained (e.g.,created, purchased, used, modified, etc.) and deployed to the computersystem. To this extent, the deployment can comprise one or more of: (1)installing program code on a computing device; (2) adding one or morecomputing and/or I/O devices to the computer system; (3) incorporatingand/or modifying the computer system to enable it to perform a processdescribed herein; and/or the like.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

What is claimed is:
 1. A tandem optoelectronic device comprising: alight emitter configured to emit radiation at multiple wavelengths, thelight emitter including: a base semiconductor layer having asemiconductor heterostructure mesa located on a first surface of thebase semiconductor layer, wherein the mesa includes a plurality ofactive regions, and wherein the plurality of active regions include: afirst active region having a first main peak of radiative recombinationat a first wavelength and a first full width at half maximum; and asecond active region having a second main peak of radiativerecombination at a second wavelength and a second full width at halfmaximum, wherein the first wavelength and the second wavelength differby at least a larger of the first full width at half maximum or thesecond full width at half maximum; a light detector configured tooperate in conjunction with the light emitter; and a channel regionoperatively coupled to both the light emitter and the light detector;wherein the channel region excites a fluorescent signal in response toradiation emitted from the light emitter, wherein the light detectordetects the fluorescent signal excited by the radiation, and wherein thelight detector analyzes the detected fluorescent signal.
 2. The deviceof claim 1, wherein the base semiconductor layer includes a plurality ofphysically separate semiconductor heterostructure mesas located thereon.3. The device of claim 1, wherein the mesa further includes: a firstsemiconductor contact layer to the first active region; and a secondsemiconductor contact layer to the second active region, wherein thesecond semiconductor contact layer is located within the mesa at alocation below the first active region.
 4. The device of claim 3,wherein the mesa further includes: a first metal contact locateddirectly on the first semiconductor contact layer; a second metalcontact located directly on the second semiconductor contact layer; anda dielectric material located between the second metal contact and thefirst active region.
 5. The device of claim 1, further comprising a setof metal contacts located on the first surface of the base semiconductorlayer.
 6. The device of claim 1, further comprising a set of metalcontacts located on a second surface of the base semiconductor layeropposite the first surface.
 7. The device of claim 1, the mesa furtherincluding: an n-type semiconductor contact layer located adjacent to afirst side surface of the mesa; and a p-type semiconductor contact layerlocated adjacent to a second side surface of the mesa, wherein thesecond side surface is different from the first side surface, andwherein the n-type semiconductor contact layer and the p-typesemiconductor contact layer contact each of the plurality of activeregions.
 8. The device of claim 7, further comprising a metallic contactformed on each of the n-type semiconductor contact layer and the p-typesemiconductor layer.
 9. The device of claim 1, wherein at least one ofthe plurality of active regions includes a plurality of interlayers,with each interlayer having a composition that provides a latticemismatch with a neighboring layer.
 10. The device of claim 7, whereineach of the first and second side surfaces of the mesa forms an anglebetween approximately ten and approximately eighty degrees with normalto the first surface of the base semiconductor layer on which the mesais located.
 11. The device of claim 1, wherein the mesa includes aplurality of cavities formed therein, each cavity extending downwardfrom a top surface of the mesa to a depth that is just above one of theplurality of active regions.
 12. The device of claim 11, wherein eachcavity includes a contact layer formed in a bottom portion thereof,wherein the contact layer is form over a corresponding active region.13. The device of claim 12, wherein each cavity further includes a metalcontact formed over the contact layer.
 14. The device of claim 13,wherein each cavity further includes a dielectric material formedagainst each sidewall of the cavity, wherein the dielectric material isformed on the contact layer and the metal contact.
 15. The device ofclaim 8, wherein the mesa is configured to receive current injectedlaterally through the metallic contacts and the n-type semiconductorcontact layer and the p-type semiconductor layers.
 16. A systemcomprising: a first optoelectronic device comprising: a basesemiconductor layer having a semiconductor heterostructure mesa locatedon a first surface of the base semiconductor layer, wherein the mesaincludes a plurality of active regions, and wherein the plurality ofactive regions include: a first active region having a first main peakof radiative recombination at a first wavelength and a first full widthat half maximum; and a second active region having a second main peak ofradiative recombination at a second wavelength and a second full widthat half maximum, wherein the first wavelength and the second wavelengthdiffer by at least a larger of the first full width at half maximum orthe second full width at half maximum; a second optoelectronic device,wherein one of the first or second optoelectronic devices is configuredto be operated as an emitter and the other of the first or secondoptoelectronic devices is configured to be operated as a detector; and achannel region operatively coupled to both the first optoelectronicdevice and the second optoelectronic device, the channel region having amedium that excites a fluorescent signal in response to radiationdirected to the medium from the optoelectronic device configured tooperate as the emitter, wherein the optoelectronic device configured tooperate as the detector detects the fluorescent signal excited by theradiation.
 17. The system of claim 16, wherein the second optoelectronicdevice includes: a second base semiconductor layer having a secondsemiconductor heterostructure mesa located on a first surface of thesecond base semiconductor layer, wherein the second mesa includes asecond plurality of active regions, and wherein the second plurality ofactive regions include: a third active region having a third main peakof radiative recombination at a third wavelength and a third full widthat half maximum; and a fourth active region having a fourth main peak ofradiative recombination at a fourth wavelength and a fourth full widthat half maximum, wherein the third wavelength and the fourth wavelengthdiffer by at least a larger of the third full width at half maximum orthe fourth full width at half maximum.
 18. The system of claim 16,wherein the optoelectronic device of the first optoelectronic device andthe second optoelectronic device configured to operate as the detectoris further configured to analyze the fluorescent signal to ascertainproperties of the medium in the channel region.
 19. The system of claim16, wherein the optoelectronic device of the first optoelectronic deviceand the second optoelectronic device configured to operate as theemitter, is further configured to release a pulse of radiation having aparticular wavelength or a multiple of wavelengths at a first time, andthe other optoelectronic device of the first optoelectronic device andthe second optoelectronic device configured to operate as the detectoris further configured to detect and analyze a time dependent fluorescentsignal excited from the medium in response to the pulse of radiation,wherein the detector is configured to determine one or more attributesassociated with the detected time dependent fluorescent signal, whereinthe one or more attributes is indicative of one or more properties ofthe medium in the channel region.
 20. A tandem optoelectronic devicecomprising: a light emitter configured to emit radiation at multiplewavelengths, comprising: a substrate; a buffer layer formed on thesubstrate; a semiconductor heterostructure mesa formed on the bufferlayer, wherein the mesa includes a plurality of active regions, with atleast one active region formed from a series of alternating quantumwells and barriers, wherein the plurality of active regions include: afirst active region having a first main peak of radiative recombinationat a first wavelength and a first full width at half maximum; and asecond active region having a second main peak of radiativerecombination at a second wavelength and a second full width at halfmaximum, wherein the first wavelength and the second wavelength differby at least a larger of the first full width at half maximum or thesecond full width at half maximum; a light detector configured tooperate in conjunction with the light emitter; and a channel regionoperatively coupled to both the light emitter and the light detector;wherein the channel region excites a fluorescent signal in response toradiation emitted from the light emitter, wherein the light detectordetects the fluorescent signal excited by the radiation, and wherein thelight detector analyzes the detected fluorescent signal.